Literature Review By Irene Chen

Literature reviewbyIrene Chen

SkinSkin functionalities / Skin anatomy Mechanical properties of skin Basic properties of collagen and elastin Viscoelastic properties of skin Viscous and elastic spring constantsFinite element modeling of skin deformation Skin mechanical properties measuring devices Suction and torsion devices Skin mechanical failure Hypertrophic scar tissue Stretch mark tissueTissue engineering Animal skin mechanics Rhinoceros and eel skin material properties Muscle tissue: skeletal muscle, cardiac muscle, and smoothmuscleHierarchical organization of skeletal muscle Hills functional model Cardiac mechanics Mechanical properties of smooth muscle

Heaviest single organ of the body (16% of total bodyweight)1.2-2.3 m2 of surface area contacting externalenvironmentSkin on the back is 4mm thick and scalp skin is 1.5mmthick3 major layers: epidermis, dermis, and hypodermis layerEpidermis layer’s mechanism- prevent water loss,thermal control, and UV protectionSkin is heterogeneous, anisotropic and a non-linearviscoelastic materialRoss, Michael. Histology: A text and Atlas. Pensylvania: Wojciech Pawlina, 2003.

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Keratinocyte: are structural proteincomponents, they play a role in forming theepidermal wall barrierLangerhans’: are antigen-producing cells in theepidermis layerMelanocyte: produces melanin (pigments inskin)Merkel’s cell: cells in the epidermis layer whichrelates to sensory in skinRoss, Michael. Histology: A text and Atlas. Pensylvania: Wojciech Pawlina, 2003.

A proteoglycan matrixCollagen fibers (type I and type III): areresponsible for mechanical properties of skinElastic fibers: giving elasticity of skinBlood vessels: providing oxygen and nutrientsNervous system : having sensory purposeRoss, Michael. Histology: A text and Atlas. Pensylvania: Wojciech Pawlina, 2003.

Depends on the nature and organization of: Dermal collagen and elastic fibers networkWater, proteins and macromolecule embedded inthe extracellular matrixwith less contribution by epidermis and stratumcorneumAgache P, “ Mechanical properties and Young’s modulus of human skin in vivo”, Arch Dermatol Res 1980: 269: 221-232

300 nm long and 1.5 nm in diameterTropocollagen triple helix- consist of threepolypeptide strandsQuaternary structure (stabilized by hydrogenbonds)29 types of collagenE along fiber 1000 MPaUTS 50-100 MPahttp://en.wikipedia.org/wiki/CollagenFung, Y.C, “ Biomechanics: mechanical properties of living tissue” 2nd ed. Springer( 1993)

Collagen I: skin, tendon, vascular, ligature,organs, bone (main component of bone)Collagen II: cartilage (main component ofcartilage)Collagen III: reticulate (main component ofreticular fibers), commonly found alongsidetype I.Collagen IV: basis of cell basement membranesCollagen V: Cells surfaces, hair and placenta

Protein fibrillin and amino acids (glycine,valine, alanine, and proline)Providing elasticity- tissue are able to retractback to its shape after deformationLocation- blood vessels (Windkessel effect),lungs, skin, bladder and elastic cartilage E 0.6 MPahttp://en.wikipedia.org/wiki/ElasinFung, Y.C, “ Biomechanics: mechanical properties of living tissue” 2nd ed. Springer( 1993)

Skin exhibit both viscous and elasticcharacteristics when undergoing icity

Mechanical behavior of skin and tendon are different!This is due to differences in collagen types self-assembly, i.e.tilt angle of collagens (orientation), fiber length, volumefraction of the Fibers, collagen molecular stretchingSilver, “ Viscoelastic properties of human skin and processed dermis”, Skin research and technology 2001:7:18-23

Silver, “ Viscoelastic properties of human skin and processed dermis”, Skin research and technology 2001:7:18-23

Upon stretching, collagen fibersstraightens and realign parallelto one another Skin has non-linear viscoelastic properties Skin exhibit hysteresis loop effect with energyloss when deformation occurs Creep is a skin mechanical failure- the resultof water molecules displacement fromcollagen fibers network

Bischoff, Jeffrey, “Finite element modeling of human skin using isotropic, nonlinear elastic constitutive model”, Journal of Biomechanics

Measuring devices suction systemtorsion deviceAgache P, “ Mechanical properties and Young’s modulus of human skin in vivo”, Arch Dermatol Res 1980: 269: 221-232

Diridollou S., “In vivo model of the mechanical properties of the human skin under suction”, Skin research and technology(2000) , Vol 6: 214-221

Assumptions: skin is an isotropic elasticmembrane and the geometry of deformation isa portion of a sphere Pr 0σ 2tσ circumferential stress P ( Pext P 0)r 0 inner radius of the spheret - thickness of the skinDiridollou S., “In vivo model of the mechanical properties of the human skin under suction”, Skin research and technology(2000) , Vol 6: 214-221

Diridollou S., “In vivo model of the mechanical properties of the human skin under suction”, Skin research and technology(2000) , Vol 6: 214-221

1. Fixture on skin2. Twist of 2-6degrees3. Measure radialdisplacement4. Applied load isapproximately28.6 *10-3 NSkinAgache, P.G, “Mechanical Properties and Young’s Modulus of Human Skin in Vivo”, Journal of Dermatological Research

Agache, P.G, “Mechanical Properties and Young’s Modulus of Human Skin in Vivo”, Journal of Dermatological Research

First-degree of burns: damage on epidermislayerSecond-degree of burns: papillary dermis layer(hypertrophic scarring)Third-degree of burns: reticular dermis layerForth-degree of burns: subcutaneous layer(needs skin graft)

Scars tissue are usually thickened andinextensiblePressure therapy to progressively softeningand thinning of the scar tissueApplied pressure ranges from 10 mmHg to 35mmHgStimulate and remodel the scar tissueClark, J. A, “Mechanical properties of normal skin and hypertrophic scars”, Burns 1996: Vol. 22: p443-446

Uniaxial loading deviceClark, J. A, “Mechanical properties of normal skin and hypertrophic scars”, Burns 1996: Vol. 22: p443-446

Scaffold’s biomaterial:hyaluronan with benzyl estercells: Fibroblast-keratinocyteswere obtained from epidermisby trypsin digestion.Results: fibroblasts seededinside the three dimensionalstructure, they are able toadhere, proliferate, and secretemain ECM ingredients. Theyobserved basement membranebetween epithelial and dermallayer.Zacchi, Valentina, “ In vitro engineering of human skin-like tissue”, J Biomed Mater Res. 1998 May; 40(2): pp.187-94

Collagenous dermis- thick and protectiveshowing off: a dense and highly ordered threedimensional array of straight and highly crosslinkedcollagen fibersHigh impact resistanceSteep stress-strain curveHigh elastic young’s modulus of 240MPaTensile strength of 30MPaHigh breaking energy: 3MJm-3Work of fracture: 78kJm-2As a biological material, material properties is inbetween a cat and a human ino.jpgShadwick, Robert. “ The structure and mechanical design of rhinoceros dermal armour”, Phil. Trans. R. Soc. Lond. B(1992): 337, pp. 419-428

Polarized light micrographs oftransverse sections of whiterhinoceros skin showing collagenfibers in the deep dermis (a) theflank (b) the belly Highly crosslinked of fibernetwork for flank region skin Fibers are relatively straight andaverages around 90 μm indiameterShadwick, Robert. “ The structure and mechanical design of rhinoceros dermal armour”, Phil. Trans. R. Soc. Lond. B(1992): 337, pp. 419-428

Shadwick, Robert,” The structure and mechanical design of rhinoceros dermal armour”, Phil. Trans. R. Soc.Land. Vol. B (1992)

Skin can adjust to environmentfor protectionSecret mucus to assist in harshweatherUsed as door hinges (in Scandivia)Changes its shape to be flexiblefor necessary locomotionA system of collagen fibers in skin allow forshape changesHerbrank, M. R., “ Mechanical properties and locomotor functions of eel skin”, the Biological Bulletin 1980 (158): 58-68

Herbrank, M. R., “ Mechanical properties and locomotor functions of eel skin”, the Biological Bulletin 1980 (158): 58-68

Herbrank, M. R., “ Mechanical properties and locomotor functions of eel skin”, the Biological Bulletin 1980 (158): 58-68

Purpose: movement of the body and for deformation /undeformationof internal organsSkeletalCardiacSmoothMuscle cellLarge, elongatedcell, 10-100 μm indiameter, up to100 μm in lengthShort, narrow cell,10-15 μm indiameter, 80-100μm in lengthShort, elongatedcell, 0.2-2 μm indiameter, 20-200μm in lengthLocationMuscle of skeleton Heart, vena cava,pulmonary veins(e.g. tongue,esophagus,diaphragm)Vessels, organsFiberSingle skeletalmuscle cellLinear, branchedarrangementSingle smoothmuscle cellTypes ofcontraction“All or none”“All or none”Slow, partial,rhythmic

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Fung, Y.C, “ Biomechanics: mechanical properties of living tissue” 2nd ed. Springer( 1993)

Fung, Y.C, “ Biomechanics: mechanical properties of living tissue” 2nd ed. Springer( 1993)

Skin is multilayered and has differentmechanical properties in each layerCollagen fibers and elastic fibers arrangementgive out different material propertiesApplying mechanical stimuli to skin changesmaterial propertiesSkin tissue engineering can be doneAnimals have their unique properties ofdifferent kind of skin tissue Rhinoceros has a strong impact resistance skinEel has an flexible skin which can change due toenvironment

Prof. MeyersDr. Po-Yu ChenProf. LubardaDr. Peter Chen

Thank you for your attention!

Skin mechanical properties measuring devices Suction and torsion devices Skin mechanical failure Hypertrophic scar tissue Stretch mark tissue Tissue engineering Animal skin mechanics Rhinoceros and eel skin material properties Muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle